1. Field of the Invention
The present invention relates to a paper finisher which is integrated with, fixed on, or provided separately in an image forming apparatus such as a printer, copying machine, and facsimile machine, and performs predetermined processing on a recording medium which is discharged from the image forming apparatus. Particularly, the present invention relates to a paper perforating apparatus having perforating means for forming perforated holes on a recording medium.
2. Description of the Related Art
There has been developed numbers of paper finishers which perform processing such as sorting, stapling, folding, and perforating on papers which are discharged from an image forming apparatus such as a copying machine and printer. Regarding the perforating processing (referred to as “perforating processing” hereinafter) performed by these finishers, there is generally known a pressing method for forming perforated holes (punch holes) on papers one by one that are being conveyed. Recently, numbers of perforating apparatuses that can form various types of punch wholes (on different positions and with different hole diameters) are provided. Further, in order to improve the accuracy of jogging the papers when bundling the papers, there are further provided perforating apparatuses which are configured so as to be able to move perforating means thereof toward conveyed papers in a direction perpendicular to the paper conveyance direction.
The known forms of perforated holes are a 3-hole punching, which is generally used in North America (referred to as “North America 3-hole punching” hereinafter), and a form of 4-hole punching, which is used in Europe (referred to as “European 4-hole punching” hereinafter). In the North America 3-hole punching, each hole has a hole diameter of 8 mm and a punch-hole pitch of 108 mm. On the other hand, in the European 4-hole punching, each hole has a hole diameter of 6.5 mm, and the punch-hole pitch thereof is set such that two holes are formed on an inner side that is 40 mm distant from the center line of a sheet of paper, and another two holes are formed on the outer sides that is 80 mm distant from these two inner holes. As described hereinbefore, many perforating means that can respond to different hole positions and different hole diameters.
In the case where the abovementioned North America 3-hole punching is used as the perforating means of the paper finisher so as to be made capable of moving as described above, when setting a home position of the perforating means to a position for forming punch holes on a paper, that is, a position in which the center of each hole to be punched and the center of the conveyance direction of the paper fit together, and when conveying the paper, which is a LT (letter) size (8.5 inches×11 inches) paper widely used in North America, in a longitudinal direction, that is, in a way that the longitudinal direction and the conveyance direction of the paper are parallel to each other, a side end of the paper passes over two holes that are positioned on the outer sides of the three holes, thus the side end is caught in these holes, causing jams and curled edges many times. Similarly, in the case of the perforating means in which the European 4-hole punching is used, if a home position of the perforating means is set to a position where punch holes are formed on a paper, when conveying the paper, which is a B4 size paper widely used in Europe, in a longitudinal direction, that is, in a way that the longitudinal direction and the conveyance direction of the paper are parallel to each other, a side end of the paper passes over the holes that are positioned on the outer sides, thus the side end is caught in these holes, causing jams and curled edges.
As a measure against the above-described problems, there is proposed a method for guiding a paper end portion to the vicinity of the holes where a side end of the paper is caught, by means of a mylar sheet or the like. For example, Japanese Patent Application Laid-Open No. H7-186098 discloses a paper perforating apparatus which comprises guiding means for guiding papers in a predetermined direction, a perforating blade provided in the guiding means and punching holes on the papers, a conveyance roller provided on the downstream side of the perforating blade and constantly conveying the papers, drive means for driving the perforating blade, and idling control means for causing the drive means to operate so as to drive the perforating blade during a specific period of time when no paper is present in a perforation position in the guiding means. Accordingly, the guiding means is prevented from having the perforation position therein in a state where the perforating blade is driven incompletely, and jams that are caused by a paper being caught by the perforating blade can be prevented.
However, even when using such means, jams or curled edges may be generated depending on conditions of the paper (where the paper has a small curvature, etc), thus the above-described problems have not yet been resolved completely.